Rein Vaikmäe

A new ice-core record from Lomonosovfonna, Svalbard: viewing the 1920-97 data in relation to present climate and environmental conditions

A new ice core record from Lomonosovfonna, Svalbard: viewing the data between 1920-1997 in relation to present climate and environmental conditions

Development, structure and composition of land-fast sea ice in the northern Baltic Sea

The structural and stable-oxygen-isotopic properties of sea-ice samples collected on land-fast sea ice in the northern Baltic Sea, at 60.2-65.7° N, 21.3-26.9° E, were used to estimate the contribution of snow ice in the total sea-ice thickness, and the fraction of snow in the snow-ice layers and in the total sea-ice thickness. The textural analysis of the sea-ice cores revealed a general structure of granular surface layer and a columnar basal layer. Using different isotopic criteria to distinguish snow-ice layers, we estimate that snow-ice layers contributed on average 24 32% of the total ice thickness in the study region. Transition ice (intermediate granular columnar ice) also contributed significantly to the total ice thickness. The snow in the snow-ice layers contributed on average 18-21 % of the total sea-ice thickness (by mass), a significant contribution when compared to other regions with sea-ice cover. The methods used could be improved to give more accurate estimates, especially by improving knowledge of the temporal variability of the isotropic properties of the snow incorporated into the sea-ice cover. However, our results can be regarded. is plausible estimates for the contribution of snow ice and snow to sea-ice growth in the study area.

Pleistocene age paleo-groundwater inferred from water-stable isotope values in the central part of the Baltic Artesian Basin

ABSTRACT A new data set of δ2H and δ18O in the groundwater from the central part of the Baltic Artesian Basin is presented. The hydrogeological section is subdivided into stagnation, slow exchange and active exchange zones. Na–Ca–Cl brine found at the deepest part – the stagnation zone – is characterized by δ18O values above −5 ‰ and δ2H values approaching −40 ‰ with respect to Vienna Standard Mean Ocean Water. The slow exchange zone where waters of mostly intermediate salinity reside is characterized by δ18O values around −11.7 ‰ and δ2H values around −85.3 ‰. Mean δ18O and δ2H values of the fresh groundwater in the active water exchange zone are −11.1 and −79.9 ‰, respectively. Characteristically, the groundwater in the active and slow exchange zone is isotopically more depleted compared with the precipitation values observed, and the depletion increases with depth down to the level where strongly enriched brines are encountered.

Representing Glaciations and Subglacial Processes in Hydrogeological Models: A Numerical Investigation

The specific impact of glacial processes on groundwater flow and solute transport under ice-sheets was determined by means of numerical simulations. Groundwater flow and the transport of δ18O, TDS, and groundwater age were simulated in a generic sedimentary basin during a single glacial event followed by a postglacial period. Results show that simulating subglacial recharge with a fixed flux boundary condition is relevant only for small fluxes, which could be the case under partially wet-based ice-sheets. Glacial loading decreases overpressures, which appear only in thick and low hydraulic diffusivity layers. If subglacial recharge is low, glacial loading can lead to underpressures after the retreat of the ice-sheet. Isostasy reduces considerably the infiltration of meltwater and the groundwater flow rates. Below permafrost, groundwater flow is reduced under the ice-sheet but is enhanced beyond the ice-sheet front. Accounting for salinity-dependent density reduces the infiltration of meltwater at depth. This study shows that each glacial process is potentially relevant in models of subglacial groundwater flow and solute transport. It provides a good basis for building and interpreting such models in the future.

Assessment of paleo-recharge under the Fennoscandian Ice Sheet and its impact on regional groundwater flow in the northern Baltic Artesian Basin using a numerical model

The study investigates the mechanism of glacial meltwater recharge under the Fennosciandian Ice Sheet during the last glacial maximum (LGM) and its impact on regional groundwater flow in the northern Baltic Artesian Basin (BAB) in Estonia and Latvia. The current hypothesis is that a flow reversal occurred in the BAB due to subglacial recharge during the LGM. This hypothesis is supported by an extensive dataset of geochemical and isotopic measurements in the groundwater of northern Estonia, exhibiting significant depletion in δ18O with respect to modern precipitation. To verify the consistency of this hypothesis and better understand groundwater flow dynamics during the LGM period, a numerical model is developed for this area. Two cross-sectional models have been created across the northern BAB, in which groundwater flow and the transport of δ18O have been simulated from the beginning of the LGM to present-day. Several simulations were performed with different subglacial boundary conditions, to investigate the uncertainty related to subglacial recharge of meltwater during the LGM and the subsequent flow reversal in the northern BAB. Several simulations provide a satisfying fit between computed and observed values of δ18O, which means that the hypothesis of subglacial recharge of meltwater is consistent with δ18O distribution. The numerical model suggests that preservation of meltwater in northern Estonia is controlled by confining layers and the proximity to the outcrop area of aquifers, located in the Gulf of Finland. The results also suggest that glacial meltwater has been preserved under the Baltic Sea in the Gulf of Riga.RésuméCette étude s’intéresse au mécanisme de recharge de l’eau de fonte glaciaire sous la calotte glaciaire fennoscandienne pendant le dernier maximum glaciaire (DMG) et son impact sur l’écoulement régional des eaux souterraines dans le nord du Bassin Artésien Balte (BAB) en Estonie et en Lettonie. L’hypothèse actuelle est qu’une inversion de la direction d’écoulement de l’eau souterraine s’est produite dans le BAB en raison de la recharge sous-glaciaire au cours du DMG. Cette hypothèse est étayée par un vaste ensemble de données géochimiques et isotopiques provenant du nord de l’Estonie, montrant une déplétion significative en δ18O dans les eaux souterraines par rapport aux précipitations modernes. Pour vérifier la cohérence de cette hypothèse et mieux comprendre la dynamique de l’écoulement des eaux souterraines au cours de la période du DMG, un modèle numérique est développé. Deux coupes verticales ont été créées dans le nord du BAB, dans lesquels l’écoulement de l’eau souterraine et le transport de δ18O ont été simulés depuis le début du DMG jusqu’à aujourd’hui. Plusieurs simulations ont été effectuées avec différentes conditions aux limites afin d’étudier l’incertitude liée à la recharge sous-glaciaire durant le DMG et l’inversion de l’écoulement subséquent dans le nord du BAB. Parmi ces simulations, de nombreuses produisent des résultats satisfaisants entre les valeurs calculées et observées de δ18O, ce qui signifie que l’hypothèse de recharge sous-glaciaire de l’eau de fonte est cohérente avec la distribution observée de δ18O dans le BAB. Le modèle numérique suggère que la préservation de l’eau de fonte dans le nord de l’Estonie est contrôlée par des couches de confinement et la proximité de la zone d’affleurement des aquifères, située dans le golfe de Finlande. Les résultats suggèrent également que l’eau de fonte glaciaire a été préservée sous la mer Baltique dans le golfe de Riga.ResumenEl estudio investiga el mecanismo de recarga de agua de deshielo glacial bajo la capa de hielo fenoscandiana durante el Último Máximo Glacial (LGM) y su impacto en el flujo regional del agua subterránea en la Cuenca Artesiana del Báltico (BAB) en Estonia y Letonia. La hipótesis actual es que se produjo una reversión del flujo en el BAB debido a la recarga subglacial durante el LGM. Esta hipótesis está respaldada por un extenso conjunto de datos de mediciones geoquímicas e isotópicas en las aguas subterráneas del norte de Estonia, que muestran un agotamiento significativo en δ18O con respecto a la precipitación moderna. Para verificar la consistencia de esta hipótesis y comprender mejor la dinámica del flujo del agua subterránea durante el período LGM, se desarrolla un modelo numérico para esta área. Se han creado dos modelos de corte transversal en el norte de BAB, en los que el flujo de agua subterránea y el transporte de δ18O se han simulado desde el comienzo del LGM hasta la actualidad. Se realizaron varias simulaciones con diferentes condiciones de contorno subglacial, para investigar la incertidumbre relacionada con la recarga subglacial de agua de deshielo durante el LGM y la reversión de flujo posterior en el BAB norteño. Varias simulaciones proporcionan un ajuste satisfactorio entre los valores computados y observados de δ18O lo que significa que la hipótesis de la recarga subglacial de agua de deshielo es consistente con la distribución δ18O. El modelo numérico sugiere que la preservación del agua de deshielo en el norte de Estonia está controlada por las capas de confinamiento y la proximidad al área de afloramiento de los acuíferos, ubicada en el Golfo de Finlandia. Los resultados también sugieren que el agua de deshielo glacial se ha preservado bajo el mar Báltico en el Golfo de Riga.摘要本研究调查了末次冰期芬诺斯堪的纳维亚大冰盖下面冰川融水补给机理及其对爱沙尼亚和立陶宛波罗的海自流盆地北部地下水流的影响。目前的假设是由于末次冰期的亚冰川补给,波罗的海自流盆地出现水流逆转。这个假设得到了爱沙尼亚北部地下水中地球化学和同位素测量结果大量的数据集支持,显示出现代降水中有大量的δ18O消耗。为了证明这个假设的一致性以及更好地了解末次冰期地下水流动力学,针对本地区建立了数值模型。在整个波罗的海自流盆地建立了两个剖面模型,在模型中,模拟了末次冰期到现今地下水流和δ18O的传输。采用不同的亚冰期边界条件进行了几次模拟,以调查与末次冰期间融水亚冰期补给有关的不确定性及随后发生的波罗的海北部水流逆转。几次模拟的结果显示δ18O计算值和观测值非常匹配,这意味着融水亚冰期补给的假设与δ18O分布一致。数值模型表明,爱沙尼亚北部融水的保存受到承压层以及至位于芬兰湾的含水层出露区的距离的控制。结果还表明,冰川融水储存于里加湾波罗的海之下。ResumoO estudo investiga o mecanismo de recarga por derretimento sob o lençol de gelo da Fenoscândia durante o Último Máximo Glacial (UMG) e seu impacto no fluxo regional das águas subterrâneas no norte da Bacia Artesiana do Báltico (BAB) na Estônia e na Letônia. A hipótese atual é que uma reversão de fluxo ocorreu na BAB devido à recarga subglacial durante o UMG. Esta hipótese é embasada por um extenso conjunto de dados de medições geoquímicas e isotópicas nas águas subterrâneas do norte da Estônia, exibindo depleção significativa de δ18O comparada à precipitação moderna. Para verificar a consistência desta hipótese e entender melhor a dinâmica do fluxo das águas subterrâneas durante o período do UMG, um modelo numérico é desenvolvido para esta área. Dois modelos transversais foram criados em todo o norte da BAB, em que o fluxo de águas subterrâneas e o transporte de δ18O foram simulados desde o início do UMG até o presente. Diversas simulações foram realizadas com diferentes condições de contorno subglaciais, para investigar a incerteza relacionada à recarga subglacial de água de degelo durante o UMG e a subsequente reversão de fluxo no norte da BAB. Várias simulações fornecem um ajuste satisfatório entre valores simulados e observados de δ18O, o que significa que a hipótese de recarga subglacial de água de degelo é consistente com a distribuição de δ18O. O modelo numérico sugere que a preservação da água de degelo no norte da Estônia é controlada por camadas confinantes e pela proximidade com a área de afloramento dos aquíferos, localizada no Golfo da Finlândia. Os resultados também sugerem que a água derretida glacial foi preservada sob o Mar Báltico, no Golfo de Riga.